Chronically active Ras plays a major role in tumor progression and maintenance in many types of human cancer and, thus, has been a subject of numerous efforts at directed therapy. One such Ras-directed drug is the specific inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS, salirasib) which was designed to mimic the C-terminal farnesyl cysteine carboxymethyl ester of Ras. [Marciano, D., Ben-Baruch, G., Marom, M., Egozi, Y., Haklai, R., and Kloog, Y., J. Med Chem 38:1267-1272 (1995)]. FTS interferes with Ras membrane interactions which are crucial for Ras-dependent cell transformation and tumor growth. [Haklai, R., Gana-Weisz, M., Elad, G., Paz, A., Marciano, D., Egozi, Y., Ben-Baruch, G., and Kloog, Y, Biochemistry 37:1306-1314 (1998)].